Three phase decanting centrifuges have been developed over the years to separate solids from a slurry and to separate liquid phases, such as for example oil and water. Such centrifuges are provided by such companies as FLottweg, Centrisys, and Alfa Laval. In a typical machine, as described by FLottweg, the slurry is fed through a fixed central pipe into a distributor located in the scroll of the centrifuge. The slurry to be treated is accelerated and passes through feed ports in the scroll to the bowl.
Separation of solids from the slurry takes place in the conical cylindrical bowl which rotates at a preset speed. The slurry rotates in the bowl at the design speed and forms concentric layers or solids and liquids around the inside of the bowl. The solids in the slurry are deposited against the bowl wall under the influence of centrifugal force.
The scroll rotates at a differential speed to that of the bowl and conveys the separated solids in the direction of the conical end of the scroll. The separated solids are then discharged through openings at the conical end of the bowl. The solids then enter a stationary solids housing and are discharged down an outlet chute.
While the liquid is being clarified (i.e. having the solids removed therefrom), it flows to the cylindrical end of the bowl and overflows adjustable weir plates which determine the depth of the pond. The clarified liquid is decanted into a fixed centrate chamber where two liquid phases with different specific gravities may be separated. The two liquids (e.g. oil and water) are separated in the liquid zone (two phase) and decanted through separate discharge systems to prevent cross-contamination. An adjustable paring disc provides a pressure discharge for the heavier (water) phase. If the density difference or the quantity of the two phases changes, the paring disc allows the interface between the two liquid phases to be optimally adjusted during operation to ensure maximum purity of the liquid phases.
Unfortunately, the paring disk must be adjusted by hand while monitoring the quality of the discharge. As the mix of solids and phases of liquids changes over time, an operator must recognize the changing quality of liquids at the discharges and adjust the paring disc accordingly. With rapidly changing slurry, the operator must remain dedicated to the machine, and is not free to perform other duties.
Thus, there remains a need for a three phase decanting centrifuge which can adapt to a changing mix or recipe of a slurry and maintain a desirable separation of liquid.